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THIS SNOWPACK SUMMARY EXPIRED ON January 20, 2017 @ 11:13 pmSnowpack Summary published on January 20, 2017 @ 6:13 am

Issued by
Ben Bernall - Kootenai National Forest

Avalanche Character 1: Persistent Slab

Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

In many locations we are finding facets and depth hoar (weak-sugary snow) at the ground level. It is found primarily in areas with thin snow coverage where cold temperatures have driven the formation of these weak grains. This will create a threat to backcountry travelers in areas where this sugary layer has been covered by a cohesive slab. Based on our observations this weakness will be difficult to trigger but may result in a deep release if triggered.

To avoid this potential problem it is advised to avoid thin and rocky areas with shallow snow coverage as well as steep, exposed rib features. This problem will be most prevalant in the Purcell Range due to the thinner snowpack and colder temperatures that have dominated the weather in December and January.

Snowpack Discussion

David Thompson Search and Rescue will be hosting an Introduction to Avalanches course at the SAR Barn in Libby. The class will begin Friday the 27th at 7PM for a 2-3 hour classroom presentation and resume Saturday morning for a field day at Turner Mountian. This course is free and open to the public. For additional info contact SAR Mountain Unit Leader Terry Crooks at 293-1618.

I will be putting on a "Know Before You Go" presentation in Eureka at the Lincoln County High Auditorium on January 24th at 5:30 PM. This class will provide entry level avalanche awareness and is free and open to all ages. See you there!

On January 19th, Nate and I traveled to Flatiron Mountain with Lyndsey Clark from the "SheJumps" foundation to look at the snow and explore the terrain for the upcoming Womens Level 1 Course that is being hosted by http://www.soleexperiences.org/ . Our pit results from a north east aspect revealed 3-4" of new snow overlying last weeks surface hoar that was failing with little to no force and producing clean quality 1 shears. Although highly reactive, there currently is not enough new snow sitting on this buried weak layer to be a problem. The latest weather forecasts are not predicting much in additional snow loading at this time but it will be something to watch in the coming days.

The other significant observation of note is the depth hoar and facets that can be found at the bottom of the thin Purcell snowpack. Stability tests do not show it to be highly reactive but there is always that possibility of finding a thin spot in the snowpack where it could be triggered. Avalanches initiate from thin spots and propagate to thick areas within the snowpack so keep this in mind when assessing terrain and making travel decisions.

On Tuesday, January 17th Nate and I traveled into the North Fork Keeler area where we able to experience the incoming warm air that has been present the past few days. Stability test results showed a stable snowpack that was coated in a shiny layer of large surface hoar. This surface hoarlayer is likely buried now by 3-5" of new snow in the Western Cabinets as well, as I mentioned above this is likely not an issue unless we experience additional loading of snow over the weekend. Visual observations and snotel data revealed that the Eastern Cabinets were exposed to warmer temperatures than the surrounding ranges. This likely resulted in a breakdown of the surface hoarlayer.

DISCUSSION: A few light showers will move through the area this
morning before tapering off by later this afternoon. Dry andstable conditions with relatively mild temperatures will
develop/remain today. The next waves of minor snowfall will move
through Saturday and again Sunday.

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

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